How Can A Mongolian Blue Mark On The Penis Shaft Be Treated?

Information on a blue mark round the rim of the penis, is it normal/rare? Heard the cause is to do with blood circulation?
I am 18, discovered mark about 13/14 when pulling back my foreskin. 5"7 in height and weigh 9 and a half stone. No real medical history, operation to insert gromets into my ears to boost hearing at 6 and suffered from eczema and athsma as a child.